Apraxia of speech is a widely recognized clinical entity. However, its characterization as a phonological (aphasia) disorder or as a phonetic disorder (motor speech) is less widely agreed upon than its entity. This research will exploit recent advances in measurement techniques in physiological (movement, electromyography, aerodynamics), acoustical and perceptual sciences. These data will, in many instances, provide the first simultaneously collected data, at several system levels of the speech apraxic who is without concommitant dysarthria or aphasia. In addition to the descriptive values of this study, the proposed experiments are guided by and will address directly, current theoretical issues in speech motor control and in linguistics, with a goal of disambiguating the mechanisms for apraxia of speech. A comprehansive command of the theoretical and clinical treatment issues and literature on apraxia of speech have resulted in experimental methodologies which invoke the facilitative techniques used in treatment (nonspeech movements, rate manipulations, stimulus repetitions, stimulus modality, contrastive stress, gestural reorganization and intonation) to alter the behavior of the apraxic subject. This will be done so that each subject can serve as his own control in each experiment. These procedures will lead not only to the understanding of mechanisms of apraxia of speech, but will add to the understanding of the most effective treatment techniques available to the person with apraxia of speech. In addition to the single subject design afforded by our methodology, 3 control subject groups will aid in the interpretation of the physiological, acoustic and perceptual data from the apraxic subjects and will address more directly the specific aims of the study. A normal control group will obviate the pathologhical behaviors to be analyzed. A conduction aphasic group without apraxia of speech or dysarthria will allow comparison across measures with a purely phonological disorder. A group of ataxic dysarthric subjects without aphasia or apraxia of speech will allow comparison across measures on a purely phonetic disorder.